Transcript of "Chapter 1: A First Look at Windows 2000 Professional"

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Guide to Wireless Communications

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Objectives <ul><li>Explain how the major wireless technologies are used today - WiFi </li></ul><ul><li>Describe the applications used in wireless technology </li></ul><ul><li>List and explain the advantages of wireless technology </li></ul><ul><li>List and explain the disadvantages of wireless technology </li></ul>

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Wireless – the hype? <ul><li>Wireless communications is the next major event in the history of technology </li></ul><ul><li>Wireless communications will revolutionize how we live </li></ul><ul><li>Users will be able to access digital resources no matter where they find themselves </li></ul>

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How Wireless Technology Is Used <ul><li>Wireless refers to any device that does not use wires </li></ul><ul><li>Wireless communications refers to the transmission of user data without wires </li></ul>

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SWAP <ul><li>Shared Wireless Access Protocol (SWAP) defines wireless computer networks </li></ul><ul><ul><li>Allows wireless data and voice communication from distances up to 150 feet at speeds up to 10 million bits per second (megabits or Mbps) </li></ul></ul><ul><ul><li>Established by HomeRF Working Group, comprised of over 50 different companies </li></ul></ul><ul><ul><li>Uses wireless home networking adapter that sends data over radio waves throughout the home, as seen in Figure 1-1 </li></ul></ul>

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Bluetooth <ul><li>Uses devices with small radio transceivers, called radio modules, built onto microprocessor chips </li></ul><ul><li>Special software, called a link manager, identifies other Bluetooth devices, creates links with them, and sends and receives data </li></ul><ul><li>Transmits at up to 1 Mbps over a distance of 33 feet and is not impeded by physical barriers </li></ul><ul><li>Bluetooth products created by over 1500 computer, telephone, and peripheral vendors </li></ul>

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Piconet <ul><li>Two or more Bluetooth devices that send and receive data make up a personal area network (PAN), also called a piconet </li></ul><ul><li>Figure 1-3 shows a Bluetooth network </li></ul>Bluetooth was named after the 10 th century Danish King Harold Bluetooth, who was responsible for unifying Scandinavia

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Piconets <ul><li>A piconet is one master and at least one slave using the same channel </li></ul><ul><li>An active slave is sending transmissions </li></ul><ul><li>A passive slave is not actually participating </li></ul>

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Cost <ul><li>Chips have decreased in price to about $15 from a high of over $75 </li></ul><ul><ul><li>Not advantageous to replace a $7 cable with a $15 chip </li></ul></ul><ul><ul><li>Many think cost must come down to about $5 before Bluetooth reaches competitive advantage </li></ul></ul>

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Limited Support <ul><li>Bluetooth is caught in “chicken or egg” scenario </li></ul><ul><ul><li>Because of low market penetration, Bluetooth is not fully supported by hardware and software vendors </li></ul></ul><ul><ul><li>Users reluctant to purchase technology that is not fully supported </li></ul></ul><ul><li>Microsoft is “straddling the fence” </li></ul><ul><ul><li>Provides Bluetooth support for Pocket PC 2002 </li></ul></ul><ul><ul><li>Does not support Bluetooth in Windows XP </li></ul></ul>

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Protocol Limitations <ul><li>Major limitation is no hand-off between piconets </li></ul><ul><ul><li>Unlike cell phone switching, Bluetooth connection is broken and must be restored with new master when device moves from one piconet area to another </li></ul></ul><ul><li>Bluetooth provides less than optimal security by authenticating devices instead of users </li></ul><ul><li>Devices cannot determine how function of other devices can be used in cooperating setting </li></ul>

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Market Position <ul><li>Current position is between IEEE 802.11x WLANs and cell phones </li></ul><ul><ul><li>WLAN is preferred technology for connecting wireless devices to form network </li></ul></ul><ul><ul><li>WLAN is mature, robust, flexible, popular technology </li></ul></ul><ul><ul><li>Trend today is fewer devices instead of more, and cell phones have integrated capabilities that Bluetooth lacks </li></ul></ul>

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WLAN Applications <ul><li>Almost nonexistent until 2000, WLANs have experienced astonishing growth, with sales expected to top $34 billion by 2004 </li></ul><ul><li>WLANs have broad range of uses including colleges and schools, businesses, airports, warehouses, shopping malls, and stadiums </li></ul><ul><li>WLANs have taken the world by storm and the list of users grows daily </li></ul>

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Wireless NIC and Access Point (AP) <ul><li>Each computer on WLAN uses wireless network interface card (NIC) with built-in antenna </li></ul><ul><li>Wireless NIC sends signals through radio waves to a fixed access point (AP) </li></ul><ul><ul><li>AP point may be attached to a wired LAN </li></ul></ul><ul><ul><li>Figure 1-9 shows an AP and wireless NIC </li></ul></ul><ul><li>WLANs also used in office environments, as shown in Figure 1-10 </li></ul>

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Wireless Network Interface Card <ul><li>NIC connects computer to network so it can send and receive data </li></ul><ul><li>On wired network, NIC has a port for a cable connector, as seen in Figure 6-1 </li></ul><ul><li>On wireless network, the NIC has an antenna to send and receive RF signals </li></ul><ul><ul><li>NIC changes internal data from parallel to serial, divides data into packets with sending and receiving addresses, determines when to send packet, and transmits packet </li></ul></ul>

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Software for Wireless NICs <ul><li>Software may be part of operating system itself </li></ul><ul><ul><li>Windows XP has software integrated while previous versions of Windows do not </li></ul></ul><ul><li>Software may be separate program loaded into the computer </li></ul><ul><ul><li>All operating systems before Windows XP, including Linux, require loading software </li></ul></ul><ul><ul><li>Operating systems for PDAs may soon integrate software to recognize a wireless NIC </li></ul></ul>

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Access Point <ul><li>An access point (AP) has three main parts </li></ul><ul><ul><li>An antenna and a radio transmitter/receiver </li></ul></ul><ul><ul><li>An RJ-45 wired network interface to connect to a wired network </li></ul></ul><ul><ul><li>Special bridging software </li></ul></ul>

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Functions of an Access Point <ul><li>Access point has two basic functions </li></ul><ul><ul><li>Acts as base station for wireless network </li></ul></ul><ul><ul><li>Acts as bridge between wireless and wired network </li></ul></ul><ul><ul><li>Bridges are LAN connectors at MAC level </li></ul></ul><ul><li>See Figure 6-7 </li></ul>

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Characteristics of an Access Point <ul><li>Range approximately 375 feet (115 meters) </li></ul><ul><li>Generally supports over 100 users </li></ul><ul><ul><li>One access point for each 50 users with light email and basic Internet access </li></ul></ul><ul><ul><li>One access point per 20 users for heavy network access and large file transfer </li></ul></ul><ul><li>APs typically mounted on ceiling, but AC power may be a problem </li></ul><ul><ul><li>Power over Ethernet feature delivers DC power through standard unshielded twisted pair (UTP) Ethernet cable </li></ul></ul>

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Ad Hoc Mode <ul><li>Ad Hoc Mode or peer-to-peer mode lets wireless clients communicate among themselves without an access point </li></ul><ul><ul><li>Officially called Independent Basic Services Set (IBSS), this mode is easy to set up, but it does not have access to a wired network </li></ul></ul><ul><ul><li>See Figure 6-8 </li></ul></ul>

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Infrastructure Mode <ul><li>Infrastructure Mode, also called Basic Service Set (BSS), has wireless clients and an access point </li></ul><ul><li>More access points can be added to create an Extended Service Set (ESS) </li></ul><ul><ul><li>See Figure 6-9 </li></ul></ul>

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Features of Access Points <ul><li>Coverage area should overlap when using multiple access points </li></ul><ul><ul><li>Wireless clients survey radio frequencies to find an AP that provides better service </li></ul></ul><ul><ul><li>A seamless handoff occurs when client associates with new AP </li></ul></ul>

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ESS and Subdivided Networks <ul><li>Drawback of ESS WLANs is that all wireless clients and APs must be part of same network to allow roaming </li></ul><ul><li>Network managers like to subdivide networks into subnets, but this prevents clients from roaming freely </li></ul><ul><ul><li>Alternative may be software that tricks network into seeing subnets as one network </li></ul></ul>

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Wireless Gateway <ul><li>Devices that follow 802.11 standard are becoming less expensive and more popular </li></ul><ul><li>Wireless Gateway has made future of HomeRF very shaky </li></ul><ul><li>Wireless gateway has wireless access point, Network Address Translator (NAT) router, firewall, connections for DSL and cable modems, and other features </li></ul>

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IEEE 802.11 <ul><li>Introduced in 1990 </li></ul><ul><li>Defines cable-free local area network with either fixed or mobile locations that transmit at either 1 or 2 Mbps </li></ul><ul><li>Uses OSI model with functions of PHY and MAC layer performing WLAN features </li></ul><ul><ul><li>See Figure 6-10 </li></ul></ul><ul><li>Slow bandwidth insufficient for most network applications </li></ul>

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Physical Layer <ul><li>Physical layer that sends and receives signals from network is divided into two parts </li></ul><ul><ul><li>See Figure 6-11 </li></ul></ul><ul><li>Physical Medium Dependent (PMD) sublayer defines how data is transmitted and received through the medium </li></ul><ul><li>Physical Layer Convergence Procedure (PLCP) performs two basic functions, as seen in Figure 6-12 </li></ul><ul><ul><li>Reformats data into frame PMD sublayer can transmit </li></ul></ul><ul><ul><li>Listens to determine when data can be sent </li></ul></ul>

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Distributed Coordination Function <ul><li>Channel access methods refer to different ways of sharing </li></ul><ul><li>Contention </li></ul><ul><ul><li>Computers compete for use of network </li></ul></ul><ul><ul><li>May cause collisions that result in scrambled messages, as seen in Figure 6-14 </li></ul></ul><ul><ul><li>Must first listen to be sure no other device is transmitting </li></ul></ul>

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Point Coordination Function <ul><li>Polling, an orderly channel access method, prevents collisions by requiring device to get permission before transmitting </li></ul><ul><ul><li>Each computer is asked in sequence if it wants to transmit, as shown in Figure 6-18 </li></ul></ul><ul><li>802.11b uses an optional polling function known as Point Coordination Function (PCF) </li></ul><ul><ul><li>Beacon frame indicates how long PCF will be used </li></ul></ul><ul><ul><li>If client has nothing to transmit, it returns a null data frame </li></ul></ul>

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Reassociation <ul><li>Reassociation involves dropping connection with one access point and establishing connection with another AP </li></ul><ul><ul><li>Allows mobile clients to roam beyond coverage area of single AP </li></ul></ul><ul><ul><li>Allows client to find new AP if original one becomes weak or has interference </li></ul></ul><ul><li>Client scans to find new AP and sends reassociation request frame </li></ul><ul><ul><li>New AP then sends disassociation frame to old AP as shown in Figure 6-19 </li></ul></ul>

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MAC Frame Formats <ul><li>802.11b specifies three different MAC frame formats </li></ul><ul><ul><li>Management frames—set up initial communication between client and AP, as seen in Figure 6-21 </li></ul></ul><ul><ul><li>Control frames—provide assistance in delivering frame that contains data, as seen in Figure 6-22 </li></ul></ul><ul><ul><li>Data frames—carry information to be transmitted to destination client, as seen in Figure 6-23 </li></ul></ul>

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Summary <ul><li>Access point (AP) contains three major parts </li></ul><ul><ul><li>Antenna </li></ul></ul><ul><ul><li>Radio transmitter/receiver </li></ul></ul><ul><ul><li>RJ-45 interface to connect by cable to standard wired network by using special bridging software </li></ul></ul><ul><li>AP has two basic functions </li></ul><ul><ul><li>Acts as base station for wireless network </li></ul></ul><ul><ul><li>Acts as bridge between wireless and wired networks </li></ul></ul>

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Summary <ul><li>RF WLAN sends and receives data in two different modes </li></ul><ul><ul><li>Ad hoc mode lets wireless clients communicate among themselves without an access point </li></ul></ul><ul><ul><li>Basic Service Set (BSS) infrastructure mode consists of wireless clients and at least one access point </li></ul></ul><ul><li>Can add more access points to increase coverage area and create Extended Basic Service Set (ESS), consisting of two or more BSS wireless networks </li></ul>

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Summary <ul><li>HomeRF, also known as Shared Wireless Access Protocol (SWAP) defines how wireless devices such as computers and cordless phones can share and communicate around the home </li></ul><ul><ul><li>Home RF version 1.0 products, introduced in 2000, transmit at 1.6 Mbps </li></ul></ul><ul><ul><li>Version 2.0, released in 2001, transmits at 10 Mbps </li></ul></ul>

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Summary <ul><li>MAC layer of 802.11b standard uses association and reassociation to allow client to join WLAN and stay connected </li></ul><ul><ul><li>Association uses either passive or active scanning to determines whether wireless client or access point should be accepted as part of network </li></ul></ul><ul><ul><li>Reassociation means client drops connection with one access point and reestablishes connection with another AP </li></ul></ul>

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Summary <ul><li>802.11 standard defines three different interframe spaces (PFS) or time gaps </li></ul><ul><ul><li>Rather than being “dead space,” these standard spacing intervals or time gaps between transmission of data frames are used for special types of transmissions </li></ul></ul>

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The Wireless Landscape <ul><li>Wireless communication is standard means of communication for people in many occupations and circumstances </li></ul><ul><li>Table 1-1 summarizes wireless technologies, transmission distance, and speed </li></ul><ul><li>Figure 1-14 shows a wireless landscape </li></ul><ul><li>Job market to support wireless technology is already exploding </li></ul>

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Summary <ul><li>Wireless communications, including Internet connections and networks, are becoming standard in business world </li></ul><ul><li>SWAP connects different devices for home users </li></ul><ul><ul><li>Quickly becoming obselete </li></ul></ul><ul><li>Bluetooth connects some devices over short distances </li></ul><ul><li>WLANs – WiFi 802.11 family </li></ul>

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Summary <ul><li>WLANS are fixture of business networks </li></ul><ul><li>WLAN applications found in wide variety of industries and organizations </li></ul><ul><li>Primary advantage of WLAN is mobility or freedom to move without being connected by a cable </li></ul><ul><li>Other advantages include easier and less expensive installation, increased network reliability, and support for disaster recovery </li></ul>